The present invention relates to an image processing apparatus used in a high-definition electronic still camera which includes a solid-state image sensor such as a CCD having a large number of pixels.
FIG. 1 shows a standard signal processor used in a conventional, standard TV format electronic still camera.
In FIG. 1, reference numeral 1 denotes an electronic still camera comprising CCD 2, sample hold circuit 3 and A/D converter 4; 5, a standard signal processor for processing image data outputted from the electronic still camera 1 and generating a luminance signal and color difference signals; 6, a timing signal generator for generating timing signals such as clock signals for controlling inner circuits of the standard signal processor 5; 7 and 8, D/A converters for converting the luminance signal and the color difference signals which are digital signals into analog signals.
The standard signal processor 5 comprises one-horizontal line (1H) delay circuits 9 and 10, luminance signal processor 11, color signal processor 12, modulator 13 for modulating the color difference signals, and delay circuit 14 for delaying the luminance signal so as to synchronize the luminance signal and the color difference signals modulated by the modulator 13. Image data from the electronic still camera 1, and image data respectively delayed by the 1H delay circuits 9 and 10, are directly supplied to the luminance signal processor 11 and the color signal processor 12.
Next, the operation of the standard signal processor 5 having the above construction will be described below.
Output from the CCD 2 of the electronic still camera 1 is sampled by the sample hold circuit 3 at predetermined periods and converted by the A/D converter 4 into digital image data. The image data is directly supplied via the 1H delay circuit 9, and further, via both the 1H delay circuits 9 and 10, to the luminance signal processor 11 and the color signal processor 12 of the standard signal processor 5.
Accordingly, the luminance signal processor 11 and the color signal processor 12 respectively perform a predetermined signal processing using current image data and image data 1H prior to the current image data and image data 1H after the current image data, and generate a luminance signal and two color difference signals. The luminance signal is inputted into the D/A converter 7 via the delay circuit 14 and converted by the D/A converter 7 into an analog signal and transmitted to devices such as a recording unit and a monitor. The color difference signals are modulated by the modulator 13 using a predetermined modulation method and converted by the D/A converter 8 into analog signals and also transmitted to the recording unit, the monitors and the like. It should be noted that the digital luminance signal and the digital color difference signals can be composed and outputted as a composite signal.
Besides the standard TV format electronic still camera having the construction as described above, a high-definition electronic still camera having a CCD, the number of pixels of which is larger than the CCD 2 of the above construction, is known.
In the high-definition electronic still camera, as the number of pixels in a horizontal direction and that in a vertical direction are larger than those in the standard TV format electronic still camera, one or some of the following problems occur when the standard signal processor 5 as shown in FIG. 1 is used in the high-definition camera:
(1) The 1H delay circuits 9 and 10 are required to have the ability to process pixel information for one horizontal line. Their capacities are insufficient for the high-definition electronic still camera since the number of pixels in one horizontal line of this camera in the high-definition format is larger than the standard TV format. PA1 (2) The CCD 2 has a portion for obtaining a black level as a reference level. Since the high-definition camera has a portion for obtaining a black level at a different position and the number of pixels of this portion is different from that of the standard TV format camera, the black level obtained cannot be evaluated correctly. PA1 (3) Since periods of synchronous signals and a blanking period in the high-definition camera are different from those in the standard TV format camera, the timings of these signals cannot be correctly obtained. PA1 (4) Since the arrangement of filters (color-arrangement) of the color filter provided in the CCD of the high-definition camera is different from that of the standard TV format camera, signals cannot be correctly processed.
For these reasons, a signal processor for the high-definition electronic still camera has been provided. Alternatively, at least one process has been omitted in the camera side and the omitted process has been performed upon image reproduction. In the former case, compared with the standard signal processor 5, the signal processor for the high-definition camera should be greater in scale, which causes an economic problem. In the latter case, as the camera side cannot complete all the necessary processings before recording, the process upon reproduction becomes complicated. Further, if information is not separated into luminance information and color information at the camera side, data compression upon recording becomes difficult.